The field of the present invention is synthetic aperture radar ("SAR"), and more particularly to techniques for encoding SAR image data to reduce data storage and transmission cost.
A modern SAR system produces imagery at a high data rate. In the standard SAR image representation, the scene being mapped is partitioned into a rectangular array of pixels with a discrete level of intensity assigned to each pixel. The intensity data are explicitly saved in some prescribed sequential order, thereby retaining the location data implicitly. As a result, the total amount of data storage requirement (without any data compression) is the product of the total number of pixels for the scene and the number of bits needed to represent the entire range of intensity levels.
In many applications, the SAR images are stored for subsequent processing and evaluation. The high data rates require large data storage capacities to store the images. If the data is to be transferred over a data communication link, a large link bandwidth is required for high speed transmission of the stored imagery data. A modern SAR image exploitation system is faced with a tremendous amount of data, and must not only have the capability to process SAR imagery at a high data rate, but also to store many SAR images as reference data.
Therefore, there is an urgent need for encoding techniques that reduce the image storage requirements without significantly degrading the interpretability or reference value of the reconstructed image. Such reduction would lead to decreased complexity and decreased data storage cost for a SAR image exploitation system.
In other applications, an efficient encoding technique could make it economically feasible for an airborne (or mobile) radar processor to carry reference SAR images in their encoded form. When a reference image is required, the compressed image could be retrieved and processed to reconstruct the original image. For other applications such as radar navigation, the reference image might be used directly in encoded form. Still another consequence of an efficient encoding technique for SAR image data would be a reduction of the transmission cost of SAR image data due to reduced bandwidth.